In a wind power generation device according to the background art of the present application, a wind force is received by a blade to rotate a main shaft connected to the blade, and a power generator is driven by increasing a speed of the rotation of the main shaft by a speed-up gear.
In the speed-up gear of the wind power generation device, a roller bearing rotatably supporting an output shaft rotating at a high speed is provided. This roller bearing has, however, a problem in which its lifetime is reduced due to smearing (a phenomenon in which a seizure is caused in a surface layer) occurring on a rolling contact surface of a roller or a raceway surface of a turning wheel.